I gave a very short talk on this topic at the AALS a few years ago, but this new draft paper is a much expanded and more systematic discussion, given as a keynote address in August for the annual meeting of the Australasian Society of Legal Philosophy in Sydney. I hope it will interest some readers, and I would especially encourage those outside general jurisprudence but with some interest in the philosophy of law to take a look, since I hope it clears up some common confusions about positivism and about Dworkin's theory of law. It would be particularly salutary for constitutional theorists to realize that no positivist theory of law denies the relevance of moral considerations to the adjudication of hard cases!